IG-267-EN versión 01; 07/04/2017
13
General Instructions
ekor.rpa
Applications
2.3. Line protection with circuit-breaker
The purpose of the line protection is to isolate this part
of the network in case of fault, without it affecting the
rest of the lines. In a general way, it covers any faults that
originate between the substation, transformer substation
or switching substation and the consumption points.
Figure 2.3. Feeder protection functions in ekor.rpa-100 relays
The types of fault that occur in these areas of the network
depend primarily on the nature of the line, overhead line or
cable and the neutral used.
In networks with overhead lines, the majority of faults are
transient, which makes many line reclosings effective; in
these cases, the reclosing function associated with circuit-
breakers is used.
This is not the case for underground cables where faults are
usually permanent.
On the other hand, in case of phase-to-earth faults in
overhead lines, when the ground resistance is very high,
the zero-sequence fault currents have a very low value In
these cases, an ‘ultrasensitive’ neutral current detection is
required.
The underground cables have earth coupling capacities,
which causes the single phase faults to include capacitive
currents. This phenomenon makes detection difficult in
isolated or resonant earthed neutral networks and thus
requires the use of the directional function.
In ekor.rpa-100 units, model ekor.rpa-110, line protection
is carried out mainly by the following functions:
• 50 ≡ Instantaneous overcurrent relay. Protects against
short-circuits between phases.
• 51 ≡ Inverse time overcurrent relay. Protects against
excessive overloads, which can deteriorate the
installation.
• 51_2 ≡ Inverse time overcurrent relay II. Additional
step to protect against excessive overloads, which can
deteriorate the installation.
• 50N ≡ Instantaneous earth overcurrent relay. Protects
against phase-to-earth short-circuits.
• 51N ≡ Inverse time earth overcurrent relay. Protects
against highly resistive faults between phase and earth.
• 51_2_N ≡ Inverse time earth overcurrent relay II.
Additional step to protect against highly resistive faults
between phase and earth.
• 50NS ≡ Instantaneous sensitive earth overcurrent
relay. Protects against phase to earth short-circuits of
very low value.
• 51NS ≡ Inverse time sensitive earth overcurrent
relay. Protects against highly resistive faults between
phase and earth of very low value.
• 51_2_NS ≡ Inverse time sensitive earth overcurrent
relay II. Additional step to protect against highly
resistive faults between phase and earth of very low
value.
• 2
nd
Harm. Block ≡ Second harmonic blocking. Blocks
overcurrent units during transformer magnetisation
• 79 ≡ Reclosing relay. Enables the automatic reclosing
of lines.
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